It's not of course, but a man can dream can't he? .net isn't dying by any stretch of the imagination. But let's start with languages most people would agree ARE legacy languages:
COBOL (if you can't agree on this, end of conversation)
VB6
various assembly languages (maaaaybe the 68000 family?)
FORTRAN (starting to get controversial here since I know it's still used by some crazy science people who don't want to learn anything modern)
Smalltalk
ALGOL
Forth
I was about to add Pascal... but then noticed some crazy person is still developing Pascal in the form of freaking Delphi, and even has a port for Android phone. WTF?
So that makes me think... if I can't include Pascal, or possibly even FORTRAN, languages I've never known someone to write code for in the past 15 years, but yet there's still new releases of it in legacy languages... then what can I include? I'm sure some nutter will try to argue with me that Forth is still a viable language. COBOL.... just go away.
The better question is more likely, which languages should you really not put your career prospects on? Personally I'd list any of the above languages, but sadly not yet PHP.